Thin Layer Chromatography High Impact Factor Journals
Thin-layer
chromatography (TLC) or planar
chromatography has been widely exploited for the separation of the ecdysteroids, using both normal- and reversed-phase systems. A suitable general normal-phase solvent system to be used with colloid TLC plates is chloroform–ethanol 4:1 (v/v). For reversed-phase TLC on C18 bonded plates, methanol–water mixtures (1:1, v/v) provide good separations. The identification of ecdysteroids by TLC is usually by comparison with the Rf values of authentic standards, but direct TLC–MS and TLC–MS/MS have been described.141,142 Where quantitative high-performance TLC (HPTLC) methods have been sought, using scanning densitometry, a sensitivity of the order of 10–100 ng per spot has been obtained, which is more than adequate for most plant-derived samples. Detection in TLC is typically by fluorescence quenching, but spray reagents have also been wont to provide color reactions of varying degrees of specificity. The most widely used is that the vanillin–sulfuric acid spray, which when warmed produces a green color for ecdysone. However, the TLC method has some drawbacks. Different sterol fractions have close Rf values in TLC, which can cause mixing during scraping of TLC bands. The method is also time-consuming and laborious. In addition, preparative TLC is disadvantageous because it's a coffee recovery rate.
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